NAD S25 User Manual

Producing a five-channel power amp of sufficient power for large Home
Theatre layouts with enough reserves for lower sensitivity 5.1-channel speaker
arrays, while maintaining the Silver Series’ very high standards for sonic
excellence was a tough challenge. NAD elegantly met it with the S250, whose
five fully independent 125-watt channels supply sufficient performance, stabil­ity and reliability to earn with ease the demanding THX Ultra certification.

The S250 employs monoblock construction for each of its five channels.
Every element of each channel’s circuitry, save the power transformer, is fully
independent, eliminating inter-channel influences as a concern. Like its stereo
predecessor, the Silver Series S200, the five-channel S250 is stable and musi­cal even into "unreasonable" loudspeaker loads. An immense edition of NAD’s
unique, extremely low-noise/low-hum "Holmgren" type power transformer—
a significant advance over conventional toroid components—works in con­cert with five monoblock amplifier sections. Over 60,000 uF of storage capac­itance ensure an ample reserve of power for even the most demanding music
and film soundtracks.

Each section features pure-differential, fully Class A input and driver stage cir­cuits, and a high-current output-stage design, employing the same high speed
output devices as used in the S200 to promulgate superb dynamic quality. The
result is musical detail, impact, and soundstage stability and depth unmatched
by multi-channel amps of two and three times the S250’s price. NAD’s propri­etary Soft Clipping (defeatable) maintains sonic quality under even severe
overdrive conditions.

Individual gain adjustment for each channel promotes easy, accurate system
configuration, as does the S250’s integral 12V trigger turn-on response,
which features a sophisticated "zero crossing" triad rather than the more
common mechanical relay to promote long component life and reduced turn­on surge. The multi-channel amplifier delivers its output via very heavy-duty
"five-way" connectors.

NAD was the first company to introduce a THX certified power amplifier. It
was therefore no surprise the NAD S250 passed Lucas Films' stringent THX
requirements with flying colours. As a result the NAD S250 will handle all
dynamics with ease and yet retain every subtle detail in the most demanding
THX Dolby Surround systems.

The S250 incorporates NAD's unique defeatable Soft-Clipping circuitry for all
five channels. Any amplifier can be overdriven if too much is asked of it (play­ing too loud, exceeding the maximum output power). Under such circum­stances, amplifiers will produce extremely high levels of distortion, which,
besides sounding very unpleasant, can damage your loudspeakers. The Soft
Clipping circuit will curtail such distortion and minimise the risk of damage
to speakers. This is particularly important with AV software that often consists
of very dynamic outbursts in which, unlike music, it is difficult to hear this
potentially damaging distortion.

Ruggedness and in-system reliability are critical to successful custom-installed
systems. This amplifier utilises a combination of fuse and electronic non­intrusive protection: dependable, fail-safe, and sonically benign. Each channel
is protected against excess temperature, DC fault and loudspeaker short-cir­cuit. Most important of all, the S250’s inherently conservative, high­voltage/high-current output-stage engineering has been designed for years of
high-performance, trouble-free service.

S250 Multi-Channel Power Amplifier

•125W x 5 Continuous Power (8 ohms); all channels driven simultaneously

• 200W x 2 Continuous Power (8 ohms); two channels driven simultaneously

• Mono-block, Modular construction • Differential, Class A input circuit topology

• Low loss, massive Holmgren* toroidal mains transformer

• Input gain control for each individual channel • All inputs Gold Plated RCA

• Soft Clipping • THX certified • 12V trigger for automated ON/OFF operation

PROVISIONAL SPECIFICATIONS - NAD S250

NOTE: NAD Electronics International reserves the right to change specifications or features without notice as design improvements are incorporated.

NAD is a registered trademark of NAD Electronics International.

All rights reserved. No part of this publication may be reproduced, stored, or transmitted in any form whatsoever without the written permission of NAD Electronics International.

Dolby is a registered trademark of Dolby Laboratories Ltd. THX is a registered trademark of Lucas Film Co.

Printed in Canada. © NAD Electronics International 02/01.

Continuous Average Power Output at 8

Ω

(Min. power per channel, 20Hz - 20kHz both channels driven with no more than rated distortion)

Rated distortion (THD 20Hz-20kHz)
Clipping power
IHF power dynamic headroom at 8

Ω

IHF power dynamic power

Damping factor
Input impedance
Input sensitivity
Voltage gain
Frequency response

Signal/noise ratio

Dimensions (W x H x D)

Net weight
Shipping weight

5 x 125W (21.0dBW)
<0.05%

0.05%
+1.4dB

8

Ω

172W (22.4dBW)

4

Ω

273W (24.4dBW)

ref. 8

Ω

, 50Hz >300

rated power into 8

Ω

50k

Ω

1.1 V

29.0dB

20Hz-20kHz +0, -0.2dB

2Hz to 100kHz -3dB

ref. 1W 95dB

ref. rated power 125dB

17

1/8

x 5

3/16

x 16

3/16

"

(435 x 132 x 410mm)

41.8 lbs (19.0kg)

46.2 lbs (21.0kg)

Power Amp Section

Physical Specifications